The main focus of our laboratory is to develop new techniques in combinatorial chemistry and chemical microarray and to apply them to basic research and drug discovery. The "one-bead one-compound" (OBOC) combinatorial library method was invented by our laboratory over a decade ago (Lam et al. 1991). Since then, it has been successfully applied to the identification of ligands for a large number of biological targets (Lam et al. 1997). The OBOC method is highly efficient, especially when used with well-established on-bead binding or functional assays. Literally millions of compounds can be screened concurrently within a few days. This method has primarily been used on peptide libraries in the past, but we believe that similar success can be accomplished with small molecule bead-libraries. While the OBOC technique is the ultimate high-throughput method, a major limitation with combinatorial small molecule bead libraries is the difficulty in elucidating the chemical structure of a small molecule compound on one single bead. A rapid, sensitive, and reliable encoding/decoding methodology is necessary for full exploitation of the OBOC combinatorial method. We propose to use topologically segregated bi-functional beads with testing molecules on the outer layer of the bead and the coding molecules placed in the interior, in conjunction with a novel encoding scheme for small molecule bead-libraries which can be readily decoded by mass spectroscopy (MALDI-FTMS). We hypothesize that from such libraries we would be able to efficiently identify small molecule ligands for various intracellular protein targets, and that these small molecule ligands would be able to exert biological effects on intact cells. We plan to apply the method to the discovery of p60c-src protein tyrosine kinase (PTK) inhibitors. Specific aims of this proposal are as follows: 1. To optimize a novel encoding system, for the OBOC combinatorial small molecule libraries, that can be easily and reliably decoded by mass spectroscopy and applicable to many different coupling chemistries in library synthesis. 2. To design, synthesize, and screen ten different encoded OBOC combinatorial small molecule libraries with a total of over 2 million compounds, and to identify and optimize ligands that bind to p60c-src PTK. 3. To evaluate the enzyme inhibitory activity and cellular effects of the identified p60c-src PTK ligands.